Method of forming cover sheet in opening of rotary electric device

Abstract

A method of forming a cover sheet over an opening of a rotary electric device such as a trimmer capacitor or a variable resistor. The rotary device includes a rotor located in a housing or case which is accessible through the opening and adjustable by a screwdriver or similar tool. To form the cover sheet, pliable resin is extended while in an unhardened state to form a film. The case is pressed against the film to introduce a part of the film into the opening. Then the resin material forming the film is allowed to partially harden before the case is separated from the film. As a result, part of the film remains in the opening of the case to form the cover sheet. As the film is completely hardened a functional cover sheet over the opening is produced.

What is claimed is: 
     
       1. A method of forming a cover sheet over an opening defined in an electric device, said method comprising the steps of: forming a thin film of hardenable resin over a base plate, said resin being a thermosetting resin that is sufficiently rigid to maintain its form upon being removed from said plate before being fully hardened, and remains both elastic and heat-resistant after hardening;   pressing said electric device against said film with said opening facing said film, said electric device being pressed with sufficient force to cause at least a portion of said film to intrude into said opening and to engage inner peripheral surfaces of said electrical device which define said opening and to adhere thereto;   separating said electric device, and a portion of said film which faces and is substantially coextensive with said opening, from said base plate and from the portion of said film that is not substantially coextensive with said opening; and   hardening said portion of film which has been removed from said plate, to form said cover sheet.   
     
     
       2. A method in accordance with claim 1, wherein said thermosetting resin is a silicone adhesive. 
     
     
       3. A method in accordance with claim 2, wherein said silicone adhesive is a hot setting type of resin. 
     
     
       4. A method in accordance with claim 2, wherein said silicone adhesive is a room temperature setting type resin. 
     
     
       5. A method in accordance with claim 1, wherein said separating step is carried out when said resin is in a half-hardened state. 
     
     
       6. A method in accordance with claim 1, further including the step of removing excess and an unnecessary portion of said film located over the exterior of an outer periphery of an edge of said opening. 
     
     
       7. A method in accordance with claim 6, wherein said removing step is performed simultaneously with said separating step. 
     
     
       8. A method in accordance with claim 1, wherein said force is sufficient to cause said edge of said opening to contact said base plate to thereby sever said film. 
     
     
       9. A method in accordance with claim 1, wherein said force is controlled to ensure that an edge defining said opening is not brought into contact with said base plate to thereby assure that said film is not severed. 
     
     
       10. A method in accordance with claim 1, further including the step of conditioning the surface of said base plate to prevent said film from adhering to said base plate to thereby facilitate said separating step. 
     
     
       11. A method in accordance with claim 1, wherein said electric device includes a stationary component and a rotatable component which is coupled to and rotatable with respect to said stationary component, said rotatable component being located adjacent said opening, said film being formed to be sufficiently thick to permit said cover sheet to contact and cover a portion of said rotatable component. 
     
     
       12. A method in accordance with claim 1, wherein said electric device is a trimmer capacitor. 
     
     
       13. A method in accordance with claim 1, wherein said electric device is a variable resistor. 
     
     
       14. A method in accordance with claim 1, wherein said opening is defined by a peripheral edge of said electric device, said peripheral edge having an inclined surface along the thickness dimension of a case which encloses said electric device, said cover film being bonded to said inclined surface. 
     
     
       15. The method in accordance with claim 1, wherein said opening is defined by a peripheral edge of the housing of said electric device, said peripheral edge being step-shaped and said cover sheet being positioned at and adhering to said peripheral edge of said edge. 
     
     
       16. A method of forming a cover sheet over an opening defined in an electric device, said method comprising the steps of: forming a thin film of hardenable resin over a base plate, said resin being a thermosetting resin that is sufficiently rigid to maintain its form upon being removed from said plate before being fully hardened, and remains both elastic and heat-resistant after hardening;   pressing said electric device against said film prior to any substantial heating of said film with said opening facing said film, said electric device being pressed with sufficient force to cause at least a portion of said film to intrude into said opening and to engage inner peripheral surfaces of said electrical device which define said opening and to adhere thereto;   separating said electric device, and a portion of said film which faces and is substantially coextensive with said opening, from said base plate and from the portion of said film that is not substantially coextensive with said opening; and   hardening said portion of film which has been removed from said plate, to form said cover sheet.